GIS Files 3: Adding real-world information

3.3: Using GIS? Be selective

You can query the features in GIS map layers by selecting and viewing just those that satisfy particular criteria. How useful is that?

Performing selections on information held in spreadsheets and databases is the classical way in which computer users make sense of large volumes of data and provide answers to specific problems. Within GIS it is possible to do just the same, only with the added advantage that the results of those queries are displayed in a geographical context. So, not only can you identify which records satisfy a particular set of criteria, you can also see where they are in relation to each other.

Data stored in tables is usually very difficult to digest all at once. It is necessary to filter out relevant sets of information corresponding to a particular group of conditions. For example, imagine you are visiting a city with which you are unfamiliar. You might have a map showing the city centre and the location of all the restaurants. With GIS a range of information about those restaurants could be stored – what type of food, average cost per head, eat in or takeaway.

The GIS can help you decide which restaurant you want to visit. You are in the mood for something a bit spicy, so you decide to select Mexican restaurants. The records from the table will be identified and any Mexican restaurants in the city will be highlighted on the map screen. You can refine your search further. You are on a budget, so you do not want the bill to be too pricey: you can therefore add an extra filter to the query by requesting a list of all Mexican restaurants with a medium cost. From this selection you may also want to make sure they do takeaway. The display now shows just those records that fit your present needs and you can maybe choose which of the selections you want based on where they are in the city.

Restaurant demo

You can make this type of query as simple or as complicated as you like, as long as the data fields are there to interrogate. This ability is not unique to GIS software; many different types of information system will allow you to perform selections. However, only GIS can provide a visual representation of the location of the query results. Furthermore, GIS can apply geographical criteria to the selection filter such that objects are selected="selected" based on where they are. We will cover this in more detail in section 4.

The next section, 3.4 – Geocoding – builds on the idea of integrating tabular data by explaining the term geocoding, another favourite example of GIS jargon.

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